Inflator filter made of wrapped mesh

ABSTRACT

An improved method for fabricating a filter for use in automotive air bag inflators which comprises forming a hollow cylindrical inner core or combustion screen of filter material and outer filter layers wound outward from the surface of the core so as to be maintained in cylindrical relation thereabout. This invention is specifically directed to an improved filter which does not include a perforated support tube and relies on only the interior combustion screen for support in the final wrapping of the remaining filter structure.

This is a continuation of application Ser. No. 08/248,939 filed on May25, 1994, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to inflatable type modular occupantrestraint systems for passenger vehicles, or, as they are more commonlyknown, air bag restraint systems. More particular, this inventionrelates to an improved rigid filter assembly for use in a pyrotechnicair bag inflator and a method for manufacturing the filter assembly. Thefilter functions to cool the hot gases before they reach the air bag andserves to trap particulates and residues generated during ignition sothat they do not enter the air bag and contaminate the vehicle.

2. Description of the Related Art

The state of the art today for manufacture of passenger inflator filtersconsists of metallic screen or mesh materials which are constructed bybeing wrapped around a rigid perforated cylinder or tube which providesstrength and support for the filter. A combustion screen, which providescooling and helps retain the generant slag inside the filter, isinserted into the interior of the perforated support tube and weldedthereto. The use of a perforated support tube adds little value to thefilter assembly and/or the performance of the filter in its deploymentin air bag inflator systems. Rather, the use of the perforated supporttube requires additional assembly operations in that the filter assemblymust be clocked during manufacture and assembly of the inflator toprovide proper alignment and this adds to the cycle time and costrequired to manufacture the inflator. A filter assembly of the aforesaidtype is disclosed in U.S. Pat. No. 5,109,772 and is assigned to heassignee of the present invention.

The consistent and economical manufacture of filter assemblies forpassenger side inflators which efficiently cool and clean gas from thegas generant is of prime concern. The elimination of parts as well asprocess steps in the manufacture of such inflators has obviousadvantages and benefits. Also advantages provided to the filter inreducing the cycle time for manufacturing the inflator result in obviouseconomic savings.

SUMMARY OF THE INVENTION

An object of this invention is to provide an improved method ofmanufacturing air bag inflator filter assemblies which reduces the timerequired to manufacture a filter assembly for a passenger sideautomotive air bag inflator. Further, an object of this invention is toprovide an improved method of manufacturing a filter assembly whichreduces the number of parts required for said assembly. Another objectof this invention is to provide an improved filter assembly which doesnot require a perforated support member and thus eliminates the need forclocking the filter during manufacture and assembly into the inflatorhousing. Still another object of the invention is to provide a newimproved filter of the character described which is relatively low incost and which provides high cooling efficiency, high uptake collectionefficiency of any toxic materials or particulates contained in theexpanding gas with relatively little impedance to the flow of gas athigh velocities therethrough.

These objectives have been achieved by a novel filter element and ameans for manufacturing the same. The filter assembly includes a hollowcylindrical inner core or combustion screen having at least one open endand internal and external surfaces constructed from at least one wrap ofexpanded metal or metal wire filter material with additional wraps offilter material substantially coextending with the external surface ofsaid inner core and wound outward from said inner core such that theadditional filter wraps are maintained in cylindrical relation aboutsaid inner core without further structural support.

The filter assembly is made by forming a hollow cylinder of at least oneexpanded metal or metal wire wrap, sizing and welding said hollowcylinder to form the inner core or interior combustion screen of saidfilter assembly, wrapping the exterior surface of the hollow cylinder bydirectly contacting said surface with additional substantiallycoextending wraps of filter material wound about said hollow cylinder,and joining the trailing end of the radially most outward wrap of filtermaterial to the filter assembly by bonding means so that the outer wrapsof filter material are maintained in cylindrical relation about saidinner core.

BRIEF DESCRIPTION OF THE DRAWINGS

With this description of the invention, a detailed description followswith reference being made to the accompanying figures of drawings whichform part of the specification, and of which:

FIG. 1 is a cross-sectional view of the cylindrical filter of thisinvention showing the individual filter elements; and

FIG. 2 is a fragmented view illustrating the placement of the filterassembly in a passenger side automotive air bag inflator.

DESCRIPTION OF THE INVENTION

A filter assembly manufactured by the process of this invention is shownin the sectional view of FIG. 1. The process for making said filter unitaccording to this invention comprises cutting 30×30 mesh metal wovencloth to length, curling it into a hollow cylindrical member havingfirst and second open ends, sizing and welding to form an inner tube orcore. The 30×30 mesh is curled in a preferred method by a two rollformer, i.e. a 0.75 inch diameter steel knurled roller and a 2 inchdiameter urethane roller, 50 durometer. This two roll former rolls thewire cloth into a capture tube while the wire cloth is being formed. Twofinish roll belts assist the wire cloth all the way into the capturetube. Once the wire cloth is completely in the capture tube it is thenstripped into a sizing tube. The tube is then sized and welded togetherby resistance welding. The 30×30 mesh wire cloth tube is stripped fromthe sizing tube. The outside diameter of the 30×30 mesh inner tube canbe held constant by using the capture tube method which wraps the filterinside a mandrel as compared to wrapping the filter outside a mandrel.In a second operation, 18×18 mesh metal woven cloth and 45×170 meshmetal woven cloth are cut to length and welded together on a lay-uptable and welding machine to form a wire cloth laminate. Paper filtermaterial is then positioned to the wire cloth laminate. The leading edgeof the wire cloth laminate/paper filter subassembly is welded to theexterior surface of the formed 30×30 mesh cylindrical tube and the wirecloth laminate and paper filter are wound outward around the 30×30 meshinner tube on an outer wrap machine. The trailing edge of the radiallymost outward portion of said laminate is welded to the thus formedcylindrical filter assembly so that the wire cloth laminate and filterpaper are maintained in cylindrical relation about said core.

The thus formed cylindrical filter assembly can be resized by subjectingsaid assembly to a rotary swaging operation such as described incopending application Ser. No. 248,933, filed May 25, 1994, now U.S.Pat. No. 5,407,120 assigned to the assignee of the present invention andfiled on even date herewith. Such resizing may be desirable foroptimizing both the cylindricity, i.e. roundness and the outsidediameter of the tubular filter assembly as well as reducing scrap loss.

FIG. 1 is a cross sectional view of a preferred cylindrical filterassembly 10. As illustrated in FIG. 1, the filter comprises a hollowcylindrical core 12 and additional layers comprising second, third andfourth wraps 14, 16 and 18 of filter materials. The hollow cylindricalcore 12 is made of 30×30 mesh metal woven cloth. The wire clothlaminate/paper filter are made of 18×18 mesh metal woven cloth 14,Lydall 924 paper 16 and 45×170 mesh metal woven cloth 18. In filterassembly 10 of FIG. 1 there is provided three layers of 30×30 mesh metalwoven cloth 12 which serve to support the filter and cool gases. Sixlayers of 18×18 mesh metal woven cloth 14, three layers of Lydall 924paper filter 16 and one layer of 45×170 mesh metal woven cloth 18 makeup the wire cloth laminate/paper filter elements. The 18×18 mesh metalwoven cloth also serves to provide structure to the filter and coolgases while the primary function of the paper filter and 45×170 meshmetal woven cloth is filtering and cooling of gases. As furtherillustrated in FIG. 1, the third and fourth wraps terminate atapproximately the same point within the filter assemble.

By way of illustration and not limitation it is noted that in anoperative embodiment of FIG. 1 of the invention, the materials of whichthe filter components are made and the dimensions thereof where relevantare as indicated below:

    ______________________________________                                        Components                                                                              Function     Materials   Dimensions                                 ______________________________________                                        filter cloth 12                                                                         Combustion screen                                                                          carbon steel                                                                              30 × 30                                        holds large              mesh .011"                                           particles and            wire                                                 slag. Also pro-          diameter                                             vides some initial                                                            cooling and sup-                                                              ports the filter                                                              assembly.                                                           coarse screen                                                                           Support ceramic                                                                            carbon steel                                                                              18 × 18                              filter cloth 14                                                                         paper. Aid in            mesh .017"                                           wrapping filter.         wire                                                 Provides cooling.        diameter                                             Supports fine                                                                 screen                                                              filter paper                                                                            Filters particu-                                                                           ceramic mfd.                                           Lydall 924 16                                                                           lates. Cools gas                                                                           by Lydall                                                        flow.                                                               fine filter                                                                             Filters and cools                                                                          stainless steel                                                                           45 × 170                             screen 18 gases                    mesh                                       ______________________________________                                    

In the preferred embodiment, the 30×30 mesh, is cut to sufficient lengthto provide an inner core comprising three layers as shown in FIG. 1 andthe 18×18 mesh, the filter paper and the 45×170 mesh materials are cutto sufficient lengths and laid-up in a laminate so as to provide six,three and 1 layers respectively when wound outward around said innercore. However, different meshes, number of layers and/or additional oralternative materials could be used in the filter assembly to tailor theperformance to a given need. For example, the function of the inner tubesupport takes place at three different times. During manufacture of thefilter assembly, the tube supports the wraps of filter material whichsurround it. During the expected lifetime of the inflator the inner tubeadditionally supports the generant contained within it. During functionof the inflator, the inner tube supports and contains the slag which isgenerated as a product of combustion. Accordingly, the number of wrapsof the mesh count of the 30×30 and 18×18 mesh could be varied toincrease or decrease the structural characteristics of the filterassembly. For example additional wraps or larger wire diameters could beused to increase strength of the filter assembly. Also the number ofwraps or the mesh count of the 30×30 and 18×18 mesh could be varied toincrease or decrease the cooling characteristics of the filter assembly.For example, additional wraps, smaller weave or larger wire diameterswould increase cooling of the gas. The number of wraps or the mesh countof the 45×170 mesh metal woven cloth or the filter paper could bechanged to increase or decrease the filtering and coolingcharacteristics of the filter assembly. For example, additional wraps orsmaller weave of wire cloth would improve the filtering ability of theassembly.

It is to be further understood that stainless steel wire cloth or othermaterials e.g. aluminum, copper, etc., could be used in place of carbonsteel cloth or expanded metal filter materials could be used for makingthe filter screens. Different commercially available ceramiccompositions could be used in place of the Lydall ceramic paper, such asceramic textiles. Further, the fine screen filter element 18 could bemade of carbon steel, fine expanded metal, steel wool or woven ceramictextile materials in keeping with the spirit of the invention.

Expanded metal filter screen is obtained from Exmet Corporation and isformed by simultaneously slitting and stretching using shaped toolswhich determine the form and number of openings. A 30×30 meshreplacement using Exmet expanded metal would be specified as 8 Fe10-5/OHXF with 42% open area. A 45×170 mesh replacement using Exmetexpanded metal would be specified as 8 SS 15-5/OHXF with 13% open area.The expanded metal is identified by reference to sheet thickness inmils, metal, strand width in mils and mesh or tool designation.

The passenger side air bag inflator filter assembly of this invention,can be used in any of A number of known constructions, including theconstruction shown in FIG. 2 and illustrated in U.S. Pat. No. 4,296,084to Schneiter, which patent is assigned to the assignee of the presentinvention. The inflator 52 includes generally an outer housing 54 intowhich is inserted the wound filter assembly 36 of this invention. Anigniter 58 containing igniter granules and the appropriate ignitionsystem is then inserted into the center of the inflator 52. Gas generant60 is then loaded into the inflator 52 which is then sealed in aconventional manner known to those in the art. After ignition of the gasgenerant, the rapidly expanding generated gases flow outwardly from thecenter of the inflator 52 through the cylindrical filter assembly 36 andheat is absorbed by the filter for cooling the gases. Substantially allof the solid residual matter carried by the gas is trapped and retainedin the various wraps of filter material.

Thus, in accordance with the invention, there has been provided animproved method for fabricating filter assemblies for use withautomotive air bag inflators which reduce both the process steps andparts required to manufacture said assemblies. Use of a perforatedsupport tube requires clocking the filter screen pack during it'smanufacture around the support tube and also clocking the filterassembly into the inflator housing. Thus, there has additionally beenprovided an improved filter assembly for use in automotive air bagswhich eliminates the need for clocking the filter during manufacture ofthe filter and assembly of the inflator and thus reduces the cycle timeand steps required in manufacturing inflators containing said filterassembly.

With this description of the invention in detail, those skilled in theart will appreciate that modification may be made to the inventionwithout departing from the spirit thereof. Therefore it is not intendedthat the scope of the invention be limited to the specific embodimentsthat have been illustrative and described. Rather, it is intended thatthe scope of the invention be determined by the scope of the appendedclaims.

What is claimed is:
 1. A gas generator filter assembly having a multiplelayered or stack-up wrapped cylindrical configuration consistingessentially of:a hollow cylindrical inner core having at least one openend and internal and external surfaces constructed from at least onewrap of metal wire mesh or expanded metal filter material, andadditional wraps of different filter material emanating from and beingsubstantially coextensive with the external surface of said inner coresuch that said additional wraps are maintained in cylindrical relationabout said core without further structural support, said additionalwraps of different filter material comprise second, third and fourthwraps of filter material wrapped outward of said inner core, wherein theleading end of said second wrap is in contact with said core, theleading end of said third wrap is in contact with said second wrap, theleading end of said fourth wrap is in contact with both said second andthird wraps and wherein the trailing ends of said third and fourth wrapsterminate at approximately the same point within said assembly.
 2. A gasgenerator filter assembly of claim 1 wherein said inner core is formedof three layers of metal cloth.
 3. A gas generator filter assembly ofclaim 2 wherein said inner core is formed of three layers of 30×30 meshwoven cloth.
 4. A gas generator filter assembly of claim 3 wherein saidsecond wrap is formed of six layers of 18×18 mesh metal woven cloth,said third wrap is formed of three layers of paper filler and saidfourth wrap is formed of one layer of 45×170 mesh metal woven cloth. 5.A gas generator filter assembly of claim 1 wherein said inner core isformed of expanded metal.
 6. A gas generator filter assembly of claim 1which has been worked and resized to improve its cylindricity.
 7. A gasgenerator filter assembly of claim 1 in the asswaged condition.
 8. A gasgenerator filter assembly having a multiple layered or stack-up wrappedcylindrical configuration consisting essentially of:a hollow cylindricalinner core member having at least one open end and internal and externalsurfaces constructed from at least one wrap of metal wire mesh orexpanded metal filter material, and having additional wraps of differentfilter material emanating from and being substantially coextensive withthe external surface of said inner core member such that said additionalwraps are maintained in cylindrical relation about said inner coremember without further structural support, said additional wraps ofdifferent filter material comprising a three-ply laminate of second,third and fourth wraps filter material concentrically wrapped outward ofsaid inner core member, wherein the leading end of said second wrap isattached to the outer surface of said inner core member and overlappingcontact therewith, the leading end of said third wrap is in overlappingcontact with said second wrap, the leading end of said fourth wrap is inoverlapping contact with said third wrap and is located intermediatesaid second and third wraps and wherein the trailing ends of said thirdand fourth wraps terminate at approximately the same point within saidassembly.